Synopsis

Description

This command sets the session user identifier and the current
user identifier of the current SQL session to be user_name. The user name can be written as
either an identifier or a string literal. Using this command, it
is possible, for example, to temporarily become an unprivileged
user and later switch back to being a superuser.

The session user identifier is initially set to be the
(possibly authenticated) user name provided by the client. The
current user identifier is normally equal to the session user
identifier, but might change temporarily in the context of
SECURITY DEFINER functions and similar
mechanisms; it can also be changed by SET ROLE. The current user identifier is
relevant for permission checking.

The session user identifier can be changed only if the initial
session user (the authenticated user)
had the superuser privilege. Otherwise, the command is accepted
only if it specifies the authenticated user name.

The SESSION and LOCAL modifiers act the same as for the regular
SET command.

The DEFAULT and RESET forms reset the session and current user
identifiers to be the originally authenticated user name. These
forms can be executed by any user.

Notes

SET SESSION AUTHORIZATION cannot be
used within a SECURITY DEFINER
function.

Compatibility

The SQL standard allows some other expressions to appear in
place of the literal user_name,
but these options are not important in practice. PostgreSQL allows identifier syntax
("username"), which SQL does not. SQL
does not allow this command during a transaction; PostgreSQL does not make this restriction
because there is no reason to. The SESSION and LOCAL
modifiers are a PostgreSQL
extension, as is the RESET syntax.

The privileges necessary to execute this command are left
implementation-defined by the standard.